Add in powers that don't refer to spells and you've got a lot of what 4e monsters have, except 5e monsters are still lacking really good design in my book. Partly a problem with 5e's combat system...
Anyway, you can do a few different minion variants. Giving them a higher than 1 point kill threshold is not bad, say 1 point plus 3/5 levels rounded down, roughly. It tends to make it possible for higher level ones to survive the very most casual types of auto damage, but doesn't really make them tough enough to take a direct hit.
The key thing 4e minions had that 5e very-low-level monsters lack is the ability to survive /making/ a save.
But for that 5e BA delivers: a much-lower-level monster can still hit occasional, the damage it does may be trivial, and your minimum damage may well kill it when you do hit - so easy to deal with, but its inclusion isn't meaningless.
In 4e, minions had a specific rule: a missed attack never damages a minion, since all AEs were still attacks (saves were a duration mechanic), fireballing a bunch of minions didn't auto-kill them, some of them would remain to do a little damage or otherwise get in the way and show themselves 'relevant' in the combat. A similar rule for 5e might be applied generally: If you're making a save for 1/2 damage vs damage that's more than double your max hps, you instead take 1/2 your max hp if you save successfully.
Dragon breath weapon recharging when bloodied is silly in 5E.
Only in that there's no bloodied condition. Aside from that, pacing the use of the breathweapon is a goodish idea - whether that's by recharging at a hp threshold, on a roll, or a crit, or after a cooldown, or whatever - a dragon that could just 'nova' and breath on you three times in a row could be problematic.
Same thing if you do a 5E Warlord with at will attack granting, time to rewrite the rogue at that point. Then you need to redo the other damage dealing classes etc.
Hardly. The 5e rogue is, if anything, less of a potential issue if systematically granted attacks than the Essentials 'Thief' was. The biggest challenge to making a 5e Warlord would be in powering it /up/ enough from the 4e version to be a viable alternative to a Paladin (let alone a full caster).
...but, kludging 5e isn't really the point of the thread...
The odds of a hill giant having 9 hp legitimately in 1E are very remote. I assume you assigned the hp rather than rolled.
That's a very very weak hill giant. Sure the occasional one like that is understandable but the minion rules are silly and gamist because it implies there are alot of them like that.
They really don't. Monster 'secondary' roles were a neat little innovation. They let a monster be level-appropriate while putting up enough of a fight to take a whole party on (Solo) or stand out from the crows (Elite). Doing that in every other edition is problematic, you dial up the level/HD on a monster that much and it's other attributes - attack/damage, saves, AC, etc - outpace the party and resolving the combat becomes tedious, at best (or simply runs into TPK territory).
Minions - or mooks or popcorn, or whatever they were called in the games that first introduced the idea a decade or so before 4e - are not representing people made of glass, they're a game mechanic that represents how bad-ass the heroes are, and a nod to the fact that using the same level of granularity overandoverandoverandoveragainandagain in a game gets boring.
Killing that first orc can be exciting, killing your 998th orc, not s'much (killing your 1000th, sure, for some reason round numbers excite people), yet heroes mow through orcs. Playing through that in hideous detail is a pain, especially if the orcs can't hit back. In 1e, the 'solution' (which didn't work on orcs, so I shoulda said 'goblins,' but I feel I'm committed at this point) was to give fighters 1 attack/level vs less-than-one-HD monsters, and to take the average on large groups of contemptible foes (so 20 orcs who hit on a natural 20 attack you, you take 1 hit, that kinda thing). In 3.x the solution was WWA and Great Cleave and giving orcs greataxes. In 5e it's BA & hp inflation. Those 'solutions' /still/ had you roll hit & damage vs every orc - and still had orcs auto-erased by AEs, even if they made their save for 1/2 damage, meaning the fighter looking badass taking out large group of orcs took a lot of boring rolling to resolve, while for the MU it was resolved in one damage roll - yep, the fireball did more than double the toughest orcs' max hps, they're all dead, no need to roll forty saves.
In 4e it was minions, and you at least didn't have to roll damage, and a few of those little minions could survive AEs, to get a lick or two in.
The 'same monster' idea that hits pseudo-simulation so hard is not the issue it appears to be, either. A "1-hp Giant" just represents the chance that giant has against a high-level party - not much of one, but it can be a threat for a round or two. Against a much lower-level party the same giant could be statted out as a Standard or even a Solo... and it could be held at the same exp value, too, if you want to be pedantic/exacting about it being the /same/ monster.
